This invention relates to temperature indicators. More particularly, it relates to high temperature reversible indicators having a dot which changes from an opaque to a transparent mode as a means for indication. It is particularly useful in monitoring leaky steam traps.
Temperature indicators which utilize chemicals changing from an opaque to a transparent mode as they pass from a solid to a liquid phase, have been used in the past particularly in the human clinical thermometer industry. One example of this phenomena is set forth in U.S. Pat. No. 3,859,856, issued to Kay Laboratories. The Kay Laboratory patent shows a human clinical thermometer which has a colored backing with a plurality of chemicals disposed thereon at discreet locations. The chemicals display the characteristic of changing from opaque to transparent upon reaching certain predetermined temperatures corresponding to those in the human clinical range. Thus the colored backing is invisible below predetermined temperatures and becomes visible above such temperatures as the chemicals melt.
Another example of this phenomena is disclosed in U.S. Pat. No. 1,676,536 issued to Carl A. Ferkel. The Ferkel patent discloses a temperature indicating device having 3 compartments which house materials changing from opaque to clear at predetermined temperatures. At the bottom of the compartments are printed the words Warm, Hot and Danger indicating various levels of temperature. The Ferkel device is adapted to be attached to a pipe which may be used in a distillation process.
U.S. Pat. No. 3,580,079 issued to Abbott Laboratories discloses a disposable clinical thermometer including a plurality of windows which are made translucent by roughing its inner surfaces to diffuse light as it passes therethrough. A chemical is provided in cells which are covered by the roughened windows which melts at a predetermined temperature. When the chemicals melt, it comes into contact with the window optically smoothing the window and permitting the bottom of the cell to become visible. Temperature numbers are printed at the bottom of each cell.
U.S. Pat. No. 3,065,083 issued to Albert Gessler discloses a time-delay temperature indicator which includes a grid which is used to prevent the spread of molten materials when the device is activated.
Of particular interest herein is the use of such an indicator to monitor steam traps. The rapidly increasing costs of producing steam has resulted in a renewed interest in efficient steam trapping and better steam trap maintenance. In general, steam traps are devices which collect condensation or water from the steam lines and recirculate the water back to a boiler. Normally, a steam trap is activated when an amount of water accumulates in the trap causing a valve to open for a very short period of time thus permitting the water which has accumulated therein to flow into the return line. A minor amount of steam often escapes the steam line when this valve is open. Problems arise, however, when the valve becomes stuck open. This permits the steam to flow from the steam line into the return water line, resulting in the loss of a great deal of steam. It has been calculated that on 1978 costs for producing steam at 100 psi that a 1/2 inch leaking line results in a $30,000 per year loss.
In order to eliminate or reduce losses of this type, steam traps must be routinely checked for leaks. Many expensive and time-consuming techniques of monitoring steam traps have been used. Some of these include pressure gauges on steam supply systems and condensate receiver tanks; listening devices such as an industrial stethoscope on the steam trap and portable contact pyrometers for measuring temperatures on both sides of the traps.
Recently, devices have come onto the market which contain a small dot that responds to certain temperatures by changing colors. One example of such a device is the so-called Steam Trap Watchdog manufactured and sold by Reliance Brooks, Inc. This device is a small 1".times.4" strip which contains a small dot responding to a specific temperature by changing color. Although the application of the Watchdog device is simple and inexpensive, still this device has a number of deficiencies. For example, the color change of the device is irreversible, the different colors of the indicating dot are not easily discernable from a distance of several feet and as many as 11 different devices are needed to monitor steam line pressures ranging from 40 to 300 psi. In addition to these deficiencies, there are several common steam trapping situations in which a properly functioning steam trap could activate this device. Furthermore, since this device is irreversible the devices must be replaced any time after they are fired. Also, they might easily give a false indication that there is a problem with the steam trap since once they are exposed to the temperatures at which they fire, they continue to indicate that there is a problem. Thus, there is a need for a reversible steam trap monitoring device.
One of the major problems in the use of reversible opaque to transparent thermometers and temperature indicators which have been previously described above, particularly in steam trap monitor applications, is that unless the devices remain horizontal, the chemicals will run to the sides of their holding pocket thus showing a portion of the bottom of the pocket of one color and another portion being opaque. This is a particular problem in the steam trap monitor application where the device might be wrapped around a pipe in a vertical position, so that it is easily read. Of course, absorbent layers could be used as shown in the General Dynamics U.S. Pat. No. 3,059,474; however, this would render the device an irreversible device with all the drawbacks described above. It is, therefore, desirable to provide an improved temperature monitor which takes advantage of the opaque to transparent mode of operation without the accompanying drawbacks.